1. Field of the Invention
This invention relates to an image formation apparatus having an image bearing member and process means acting on the image bearing member.
2. Description of the Prior Art
Description will hereinafter be made with an electrophotographic copying apparatus taken as an example of the image formation apparatus.
An electrophotographic copying apparatus requires the interchange of various expendables such as supply of developer, discard of waste toner, cleaning of corona wire, etc. or disposal during unsatisfactory feeding of transfer medium and maintenance and check-up of the apparatus. Also, when the jam of a transfer medium occurs, it is necessary to deal with the jammed transfer medium. In the past, when the maintenance of the copying apparatus has been effected, there has been an undesirable possibility that a hand or a tool may touch the surface of the image bearing member and injure that surfaces.
Usually, when maintenance is effected, that front door or the like of the apparatus is opened or the apparatus body is divisionally opened in the vertical direction, but this has led to the undesirable possibility that extraneous light enters into the copying apparatus body so that the surface of the image bearing member, particularly the surface of the image bearing member in the image transfer area is exposed to light which deteriorates the photosensitive layer of the image bearing member where the image bearing member has such photosensitive layer.
Further, recently, as shown in U.S. Pat. No. 3,985,436, it has been considered to construct a kit in which the image formation means such as a photosensitive drum, a developing device, a cleaner, a charger, etc. are made into a unitary structure and to interchange the various units at a time during interchange of the photosensitive drum, thereby reducing the maintenance work. By adopting the above-described construction, the user can simply interchange each process unit which particularly requires periodical maintenance, thus reducing the maintenance work to be done by the service man. Further, by interchanging the kit with a process kit which contains toner of another color, formation of colored images becomes possible. Alternatively, by interchanging the kit with a process kit which incorporates other developing means, the user can use developing means corresponding to the original image to be copied.
However, when the kit is interchanged or when the kit is removed from the apparatus body, the hand may touch the photosensitive drum held by the kit to stain or injure the drum. Possibly, the photosensitive drum having, for example, a zinc oxide photosensitive layer or an organic semiconductor photosensitive layer as the image bearing member held by the kit may be exposed to light with a result that the photosensitive layer is deteriorated. The injury or stain on the photosensitive drum or the deterioration of the photosensitive layer may adversely affect the formed images.
Particularly, where a process kit is used, the kit is often interchanged for the purpose of preservation or for the purpose of interchange with a process kit containing therein toner of another color as previously described, even during a period in which the kit is usable, and therefore it is necessary to positively protect the photosensitive drum.